Background: The Global Assessment of Functioning (GAF) is a widely used measure of psychiatric symptoms and functioning, yet numerous concerns persist about its reliability and validity. The objective of this study was to determine the extent to which GAF scores reflect physician-related differences in addition to information about patients. Methods: This is a secondary analysis of clinical data collected between 2005 and 2010 from inpatients at a psychiatric hospital (N = 1,852). Multilevel modeling was used to estimate the influence of physicians on GAF scores at admission and on the change between admission and discharge, controlling for patient clinical presentation. Results: Controlling for patient-level predictors, 7% of the residual variance in admission GAF scores and 8% of the residual variance in change scores was at the physician level. The physician-level variance was significantly larger than zero in both models. Conclusions: Although statistically significant, estimates of physician-level variance were not overwhelming, suggesting that the GAF was rated in a consistent manner across physicians in this hospital. While results lend support to the utility of the GAF for drawing comparisons between patients seen by different physicians across a large institution, further study is necessary to determine generalizability and to assess differences across multiple institutions.